C++ public: static field error

**Bingo90** · 04-05-2014

I'm trying to create a public and static filed in a class called ResourceManager. But when trying to access the field even from inside the class it wont work. I'm getting this error message:

Error 1 error LNK2001: unresolved external symbol "public: static int ResourceManager::num" (?num@ResourceManager@@2HA)

Here's my code:

ResourceManager.h

Code:

    class ResourceManager
    {
        public:
            static int num;
            static void loadContent();
    };

ResourceManager.cpp

Code:

#include "ResourceManager.h"


void ResourceManager::loadContent()
{
    num = 0;
}

I'm using Visual Studio 2012.

**grumpy** · 04-05-2014

Static variables need to be defined (exactly once in your program). Your code declares it (tells the compiler it exists and what type it is) but does not define it (make it exist).

Add this line to your ResourceManager.cpp after the #include "ResourceManager.h" line, at file scope.

Code:

int ResourceManager::num = 0;

The initialisation to zero is optional (as it is the default for static ints).

Don't place that line in the header file as, if the header file is #include'd by more than one source file, it will be multiply defined. That is a violation of the "one definition rule" according to the standard. Practically, it usually results in the linker complaining about a multiply defined symbol, rather than an unresolved (or undefined) one.

**Bingo90** · 04-05-2014

Ok thank you

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